Apparatus and method for lapping gears



Dec. 6, 1938. v w F, SLQMER 2,139,290

APPARATUS AND METHOD FOR LAPPING GEARS Filed Sept. 25, 1933 2 Sheets-Sheet 1 Maw? , Dec. 6, 1938. w P SLOMER 2,139,290

I APPARATUS AND METHOD FOR LAPPING GEARS Filed Sept. 25, 1933 2 Sheets-Sheet 2 a Patented Dec. 6,1938

UNITED STATES PATENT OFFICE William F. Slomer, Detroit,,Mich., assignor to The Fellows Gear Shape: Company, Springfield, Vt., a corporation of Vermont I Application September 23, 1933, Serial No. 690,715

"1' Claims.

5 mined characteristics and dimensions until brought to the prescribed accuracy and perfection of form, dimensions and surface finish; In the course of carrying out the treatment above 'dem scribed two or more master gears are usually'proand either the work piece or one of the master gears may serve as the driver; the pressure applied in then overcoming the resistance of the driven gear, which resistance may be augmented by a brake if desired, providing whatever pressure is needed between the contacting faces of the master gears or tools and the work to perform the effect required on the work. It is also the common practice to reciprocate the work piece axially at a more or less rapid rate during rotation in order better to distribute the efiect.

The object of the present invention is to provide means capable of not only finishing gears in the manner above described but also of giving a crowning formation to the gear teeth at the same time. It has been recognized in the mechanical arts in which gears are used, and particularly in the automobile art, that if gears could be made with teeth crowning from end .to end, that is, with greater thickness in the middle portion than at the ends, and with a generally convex longitudinal curvature at their faces, distinct advantages would result therefrom. Attempts have been made to produce gears of such crowning tooth formation in various ways and with greater or less measure of success. The purpose of my invention is to provide an exceedingly simple means of obtaining this result. I have discovered a radically novel means and methodfonobtaining the desired crowning efiect, which has the practical advantage of extreme simplicity and of involving no additional'step or operation in the gear finishingprocedure, nor any increase in the cost of finishing a gear. The procedure can be carried out in connection with the ordinary process of lapping, and when so carried out results in teeth having faces which to all intents and pur- Poses are crowned with a substantially uniform convexity from end to end and with a sufilcient degree of convexity and difference of thickness at points spaced apart from end to end, to givethe desired freedom of mesh with companion gears and automatic compensation for a. moderate degree of misalinement of the gears.

The basis of the invention is my discovery that 'vided for simultaneous mesh with the work piece the results above described may be accomplished by grooving circumferentially and centrally one or more (but not all) of the master gears or tools used for gear lapping; and the invention for which I claim protection consists .in the industrial utilization of this discovery in tools having a suitable grooved formation and the combination of such a tool or tools with ungrooved tools, and in the procedure of treating gears with the aid of such tools.

Referring to the drawings, Fig. 1 is a diagrammatic elevation of a se of gearlapping tools in association with a gear being lamied, containing the mechanical features, and being operated in accordance with the method phase, of this invention;

Fig. 2 is a vertical section taken on line 2--2 of Fig. 1; and shown on an enlarged scale;

Fig. 3 is a cross section taken on the broken line 3--A3 of Fig. 1;

Fig. 4 is a diagrammatic perspective view showing illustratively suitable mechanical means for imparting the necessary movements of rotation and axial reciprocation to the work and tools;

Likereference characters designate the same parts wherever they occur in all the figures.

In these drawings, W represents the work piece,

that is, a gear wheel or pinion of any character capable of being finished by lapping; and T, 'I and T represent three lapping tools, which are master gears of suitable pitch, tooth spacing, and pressure angle, to mesh with and perform the required lapping action on the work piece. In accordance with common practice these master ears are here shown as being of larger diameter than the work piece; and the work piece is reciprocated axially at the same time that it is rotated.

Although the invention involves nothing new in the principles of the machine by which the tools and work piece are supported and driven, I have deemed it advisable by way of illustration to show the main features of a machine suitable for the purpose. Such a machine is shown in Fig. 4. The work piece is mounted on a telescopic shaft consisting of the rotatable driving section S and the enveloping sleeve section 8*, such sections being splined together. The tools are mounted on parallel shafts S S and S mounted to turn in their bearings when driven by the work piece meshing with the tools, and being equipped if desired with any' suitable form of brake to increase theirresistance to rotation and consequently the pressure exerted by their tooth faces on those of the work piece. For clarity of tools are about twice as wide, and the grooves about half as wide-as the work piece; while the* illustration the tool 'I? and its shaft 8 are shown only bydotted lines in this view. A motor M drives by a belt and pulley gearing P, B and P, a power shaft S which drives the shaft section S through helical gears G, G, and so drives the work piece, which in turn drives the master gears or tools. Gear G drives a second helical gear G on shaft S", and the latter drives a shaft S through helical gears G G The latter shaft carries a crank pin which oscillates a rock shaft R by means of a connecting rod C and rock arm speed of the work may be made of any. desired value.

In carrying into eflect my present invention I provide at least one of the lapping tools with a circumferential groove. As a matter of fact in the present illustration two of the tools,-namely,

T and T are thus grooved, the groove for the tool.T' being shown at U in Fig. 3, and that of the tool T being shown at U in Fig. 2. Both grooved tools are also shown in Fig. 4. These rooves are located in the outer circumference of their respective tools and in the zone approximately midway between the ends of the tool. The width of the groove is determined in'proportion to, the width of the tool (or rather the length of the tool in its axial direction), the length of the work piece; and the extent of reciprocating motion of the work piece so that the lapping action of the grooved tool will be limited or concentrated to the ends of the work piece with no action, or a less action, at the middle of the work piece and progressively greater action from the middle to both ends. In this illustration the workpiece is reciprocated between limits coinciding approximately with the end planes of the tools, indicated by dotted lines in Figs. 2 and 3. But at least one of the tools, as T, has no' groove and acts uniformly over the whole length of the'work piece. It is within my-contemplation to groove only one of the tools; and also to provide grooves of different widths in different tools, when two or more of the tools are grooved. The absolute width of the groove is a value which may be varied considerably, a's-may be also the len th of reciprocative movement of the work, and the other dimensions of the work and tools. By properly selecting these dimensions and values desired eflects, within wide limits, of crowning the teeth of the work piece may be secured and work turned out of which the teeth are Pe ceptibly thicker at the middle than at the ends with a gradual diminution of thickness from the middle to. the ends and withoutabrupt steps between zones of diflerent thicknesses. To obtain these eifects it is necessary that the relation between thelength of reciprocative travel, the length of the-work piece teeth, and the length of-the active parts of the tool on opposite sides ,iof the groove be such that less than the whole lengtliof the 'work piece teeth be traversed across either active part of the tool; in other words,

that the reciprocation be arrested while the trail Each active part above referred to of the grooved tool may be considered as itself-a tool operating on the work piece teeth from one end to points short of the other -'end; the material of the tool inside of the groove being a connecting element which prevents either active portion from shifting out of register with the work piece while the latter meshes only with the other active portion.

The same principles and substantially identical means are equally applicable to producing crowned helical gears as well as spur gears; by using helical master gears as the lapping tools.

What I claim and desire to secure by Letters Patent is: v

1. The method of finishing gear teeth with a crowning formation which consists in rotating the gear tobe finished in mesh with a plurality of master gear laps, one of such laps being formed to limit the bearing of its teeth on the 'work'to the end portions of both sides of such teeth, and with 'an interruption of bearing on their-mid portions, while the othertool has substantially continuous bearing contact'from end to end of its teeth, and reciprocating the work piece axially in a path which causes its teeth to be engaged mainly at the end portions with one of the tools and at both ends and middle portions with the other tool.

2. A gear lapping apparatus comprising I a series of master gears adapted to make simultaneous meshing engagement with a work piece, one of said tools having an enveloping groove intersecting its teeth lintermediate' their ends,

and means for reciprocating the workpiece equally to opposite sides of a mid position wherein its middle zone coincides with such. groove: said reciprocating means being organized to'limit the travel of the work piece to a distance less than the full length of its teeth in either direction from such mid position.

3. A gear finishing apparatus comprising a series of ,master gears arranged for simultaneous meshing engagement with a centrally located work piece, and means for reciprocating a work piece in simultaneous mesh with said master gears, one of the gears having a circumferential groove intersecting its teeth intermediate their ends, and said reciprocating means being organized to arrest the work piece at each end of its'travel with its following endoverlapping the groove.

4. A gear finishing apparatus comprising .a series of master gears arranged for simultaneous meshing engagement with a centrally located work piece, means for rotating, and means for reciprocating a work piece in simultaneous mesh a circumferential groove its teeth 76 amazon crowning formation which consists in running such teeth in mesh with a plurality of master gear lapping tools, effecting relative axial reciprocation between the work piece and tools, causing one tool to act substantially uniformly over the whole length of the teeth being finished,

and causing another tool to act with greater eflect at and-near the ends of said teeth than at the middle thereof, simultaneously on opposite sides of each tooth in turn.

'1. The method of finishing gears with teeth of crowning formation which consists in running such teeth in mesh with a master gear tool, efiecting relative axial reciprocation between the work piece and tool, and limiting the extent of contact between the tool and work so that the action of the tool is applied with greater concentration at and .ne'ar the ends than at the middle part 01 the teeth being finished simultaneously on opposite sides of each tooth in turn.

. WILLIAM F. SLOMER. 

